Link

A Road on the Long Ridge - In search of an Ancient Highway on the Eiscar Riada by Hermann Geissel.
This is a free pdf book based on the TG4 program about a journey on the Eiscar Riada or Sli Mor from Dublin to Galway.
It is a great read and he also proposes that Early Christain sites were constructed beside the road for access etc.
It could also be argued that perhaps some of these were based on early prehistoric sites and therefore sites were located near the road.
It also has a section on Croghan Hill and it mentions the alignment of the Hill of Uisneach - Croghan Hill on Winter Solstice Sunrise.